 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.texteditor.quickdiff.compare.equivalence;

 import java.util.ConcurrentModificationException ;

 import org.eclipse.core.runtime.Assert;

 import org.eclipse.jface.text.source.ILineRange;

 import org.eclipse.ui.internal.texteditor.quickdiff.compare.rangedifferencer.IRangeComparator;

 /**
  * Implements the <code>IRangeComparator</code> interface for lines in
  * a document. A <code>DocEquivalenceComparator</code> is used as the
  * input for the <code>RangeDifferencer</code> engine to perform a
  * line oriented compare on documents.
  * <p>
  * A <code>DocEquivalenceComparator</code> uses a
  * <code>DocumentEquivalenceClass</code> to compare ranges.
  * </p>
  */
 public final class DocEquivalenceComparator implements IRangeComparator {

     private final DocumentEquivalenceClass fEquivalenceClass;
     private final int fLineOffset;
     private final int fLines;

     private boolean fSkip= false;
     
     public DocEquivalenceComparator(DocumentEquivalenceClass equivalenceClass, ILineRange range) {
         fEquivalenceClass= equivalenceClass;
         if (range == null) {
             fLineOffset= 0;
             fLines= fEquivalenceClass.getCount();
         } else {
             fLineOffset= range.getStartLine();
             fLines= range.getNumberOfLines();
             Assert.isTrue(fLineOffset >= 0);
             Assert.isTrue(fLineOffset + fLines <= fEquivalenceClass.getCount());
         }
     }

     /**
      * Returns the number of lines in the document.
      *
      * @return number of lines
      */
     public int getRangeCount() {
         return fLines;
     }

     /**
      * Returns <code>true</code> if a line given by the first index
      * matches a line specified by the other <code>IRangeComparator</code> and index.
      *
      * @param thisIndex the number of the line within this range comparator
      * @param other the range comparator to compare this with
      * @param otherIndex the number of the line within the other comparator
      * @return <code>true</code> if the lines are equal
      */
     public boolean rangesEqual(int thisIndex, IRangeComparator other, int otherIndex) {
         if (other instanceof DocEquivalenceComparator) {
             DocEquivalenceComparator dec= (DocEquivalenceComparator) other;
             try {
                 Hash ourHash= getHash(thisIndex);
                 Hash otherHash= dec.getHash(otherIndex);
                 return ourHash.equals(otherHash);
             } catch (ConcurrentModificationException e) {
                 fSkip= true;
             } catch (IndexOutOfBoundsException e) {
                 fSkip= true;
             }
         }
         return false;
     }
     
     Hash getHash(int index) {
         return fEquivalenceClass.getHash(fLineOffset + index);
     }

     /**
      * Aborts the comparison if the number of tokens is too large.
      *
      * @param length the current edit distance
      * @param max the maximal edit distance
      * @param other the comparator with which to compare
      * @return <code>true</code> to abort a token comparison
      */
     public boolean skipRangeComparison(int length, int max, IRangeComparator other) {
         return fSkip;
     }
 }


